Method of growing piezoelectric crystals



Patented Oct. 28, 1 952 V METHOD OF GROWING PIEZOELECTRIC CRYSTALS) Marie Bruzau, Paris, France, assignor to Inter national Standard Electric Corporation, New

' York, N. Y., a corporation of Delaware No Drawing. Application July 23, 1947,

No. 763,'164. 1 In France July 31, 1945 Serial Section 1; Public Law 690, August'8, 1946 Patent expires July 31, 1965 3 Claims. (01. 23-302) The present invention relates to piezoelectric systems, and more particularly to the production of artificial piezoelectric crystals.

It is of prior knowledge through various writ- 2 prising approximately 1500 grams of water, 500 grams of potassium phosphate (PO4H2K) and 27 grams of potassium borate. A seed crystal of potassium dihydrogen phosphate was suspended ings that numerous salts possess piezoelectric 5 in this saturated solution at about 50 to 70 0., properties, but they generally occur in the form the crystal being supported by one or more of crystals of too small a size to be serviceable hairs and being preferably directed so as to have for industrial uses; such as; in the art of teleone point face downward. cogimunfictagiong. t f th v t 1 'Icihe teinlpegatire of the sliflltlori; is grogorestsiggneo eo ecso isinvenionis oproy iminise a aconroeraeo aou duce crystals of piezoelectric substances of suffiper diem. After a period of about six and one cient size and purity to be employable for the half months or thereabouts, it is found that a above-mentioned and other purposes. large crystal growth is formed upon the seed According to features of the invention, the crystal and this crystal growth is structurally forniization of irrysitalis 8f compalrit form and sufliufiifiorm Tciystallinte 1potassium ighfydrogielrli plhotscien size is e co e y crys a ma ion 0 a sa p a e. is crys a is remove rom e a h urated solution that contains certain additional in the usual manner, dried and then can be subprgtducts. h k h b d t 6h dixgideil a3 suited1 fgr spiecific applications in esearc wor as een carrie ou W1 varop ica an iezoe ec ric evices. ious substances and particularly with monopotas- The seed rystal used is potassium phosphate sic phosphate (POHZK) which has piezoelectric (Pod-12K). The crystals resulting from the properties, as pointed out by S. B. Elings and P. crystallization process have been found to be Torptra in Zeitschrift -fiir Krystallographie, free of the borate except for possible spectrop IsI 82, vohlo'l of1t1928. t H th f f sccla taic gracgs Whigh1 riazhbe present; 1liiytojcgzlusion.

owever, 1s sa crys a izes in e orm o is. un amen a o e process a e crysfine needles thatJ are unserviceable for the uses tallization stimulating substance and the salt under considera ion. It has already been disused must have an ion in common. The role of closed that in alkaline solutions it crystallizes the potassium borate maybe said to be twointo prisms of more compact form (L. Standenfold; maier, Zeitschrift fi'ir anorganische Chemie, (1) The ions BO and K+ introduced have 1394, page 385). But neither are the an action favorable to the production of large ry tals us obtained s s y for t crystals. Experimentation has proven that the poses mentioned. presence in the solution of an excess of ions K+ Various processes have be n i v st that is favorable to the production of crystals which wou d P u el hs edg g's a sf c y gpossess characteristics favorable for piezoelectric tion, particular y y e a 1 ion 0 oreigns s1 applications. stances to a saturated solution that is made to 2 t produces a i ti of th hydrogen crystalli e O a m y reduction of the ion concentration pH of the bath. It has been p r r y evaporation found, pursuant to this invention. that the ford To; fagilitatfi tahfulleltandfntilcire c0mpt ete mation of the desired large crystals is favored ers n ing 0 6 ma 0 is lnven 1011 an b maintainin the h dro en ion concentration how the invented process can advantageously be the 501M105 at abgut S f the Solution practiceli-r a Specific embodiment p i in which the crystal is grown has a lower hydroly the piiepamtion Crystalline polasslum t gen ion of concentration than pH 5, i. e., is more drogen phosphate W111 now be descnbed but It i acidic, the desired large crystals will not form, clearly to be understood that this example is t provided by Way of illustration and not by Way but instead the material wilcrys a 1Z8 as ex of limitation, since conceivably the various astremelxfine needles unsmted for plezoelectric pects and modifications of the specific embodiappllcatlfmsment will become readily apparent to one skilled What IS claimed is: in the art, 1. Process for manufacturing abnormally large According to the present invention, potassium crystals suitable for optical and piezoelectric uses, borate is added to a saturated solution of potasthat comprises regulating growth of said cryssium phosphate. In one embodiment, the aptals from a germ crystal of potassium phosphate plicant has used with success a solution comin a super saturated solution of the acid salt-of potassium phosphate, also containing in a dissolved state, the borate of the same metal.

2. Process for manufacturing abnormally large crystals suitable for optical and piezoelectric uses, that comprisesthe steps of suspending a germ crystal of potassium phosphate in a heated and supersaturated solution of the acid salt of po-- tassium phosphate, also containing in a dissolved state, the borate of the samemetal 'and'fgradw; ally lowering the temperature of said solution 'loil over an extended period of time.-

3. Process for manufacturing abnormallytlarge crystals, suitable for optical and. piezoelectric uses, of potassium phosphate, that comprises slowly growing the crystals'in the'aqueous bath supersaturated with the dissolved acid-'salttof potassium phosphate and also containing,;in .diSH' MARIE BRUZAU.

REFERENCES CITED The following references are of record in the file-:ot this. patent:

UNITED 'STATES PATENTS Number Name Date 15: 1,75, 3,15? Booth May 20, 1930 2,452,576 Kjellgren Nov. 2, 1948 2,484,829 1' Holden Oct. 18, 1949 

1. PROCESS FOR MANUFACTURING ABNORMALLY LARGE CRYSTALS SUITABLE FOR OPTICAL AND PIEZOELECTRIC USES, THAT COMPRISES REGULATING GROWTH OF SAID CRYSTALS FROM A GERM CRYSTAL OF POTASSIUM PHOSPHATE IN A SUPER SATURATED SOLUTION OF THE ACID SALT OF POTASSIUM PHOSPHATE, ALSO CONTAINING IN A DISSOLVED STATE, THE BORATE OF THE SAME METAL. 